The present invention relates to silica-filled halogenated butyl elastomers, such as bromobutyl elastomers (BIIR).
It is known that reinforcing fillers such as carbon black and silica greatly improve the strength and fatigue properties of elastomeric compounds. It is also known that chemical interaction occurs between the elastomer and the filler. For example, good interaction between carbon black and highly unsaturated elastomers such as polybutadiene (BR) and styrene butadiene copolymers (SBR) occurs because of the large number of carbon-carbon double bonds present in these copolymers. Butyl elastomers may have only one tenth, or fewer, of the carbon-carbon double bonds found in BR or SBR, and compounds made from butyl elastomers are known to interact poorly with carbon black. For example, a compound prepared by mixing carbon black with a combination of BR and butyl elastomers results in domains of BR, which contain most of the carbon black, and butyl domains which contain very little carbon black. It is also known that butyl compounds have poor abrasion resistance.
Canadian Patent Application 2,293,149 shows that it is possible to produce filled butyl elastomer compositions with improved properties by combining halobutyl elastomers with silica and specific silanes. These silanes act as dispersing and bonding agents between the halogenated butyl elastomer and the filler. However, one disadvantage of the use of silanes is the evolution of alcohol during the process of manufacture and potentially during the use of the manufactured article produced by this process. Additionally, silanes significantly increase the cost of the resulting manufactured article.
Co-pending Canadian Patent Application 2,339,080 discloses filled halobutyl elastomeric compounds containing certain organic compounds having at least one basic nitrogen-containing group and at least one hydroxyl group enhance the interaction of halobutyl elastomers with carbon-black and mineral fillers, resulting in improved compound properties such as tensile strength and abrasion (DIN).
The present invention provides a process for preparing compositions containing halobutyl elastomers, at least one mineral filler and at least one silazane compound. The invention also provides filled halobutyl elastomer compositions comprising halobutyl elastomers, at least one mineral filler and at least one silazane compound. Preferably, the present invention provides a means to produce such filled compositions without the evolution of alcohol, and at significantly reduced cost, compared to processes known in the art.
Surprisingly, it has been discovered that silazane compounds enhance the interaction of halobutyl elastomers with mineral fillers, resulting in improved compound properties such as tensile strength and abrasion (DIN). Silazane compounds are believed to disperse and bond the silica to the halogenated elastomers.
Accordingly, the present invention also provides a process, which includes mixing a halobutyl elastomer with at least one mineral filler, in the presence of at least one silazane compound, and curing the resulting filled halobutyl elastomer. According to the present invention, the resulting filled halobutyl elastomer has improved properties.
Additionally, it has been found that mixtures of silazane compounds and an additive containing at least one hydroxyl group and a functional group containing a basic amine enhance the interaction of halobutyl elastomers with mineral fillers, resulting in improved compound properties such as tensile strength and abrasion resistance (DIN).
Accordingly, the present invention also provides a process which includes mixing a halobutyl elastomer with at least one mineral filler, in the presence of at least one silazane compound and one additive containing at least one hydroxyl group and a functional group containing a basic amine, and curing the resulting filled halobutyl elastomer. The resulting composition, having improved properties, forms another aspect of the invention.
The halobutyl elastomer, which is admixed with the mineral filler and the silazane compound or the mixture of silazane compound and an additive containing at least one hydroxy group and a functional group containing a basic amine, may also be in a mixture with another elastomer or elastomeric compound. The halobutyl elastomer should constitute more than 5% of any such mixture. Preferably, the halobutyl elastomer should constitute at least 10% of any such mixture. In some cases it is preferred not to use mixtures but to use the halobutyl elastomer as the sole elastomer. If mixtures are to be used, the other elastomer may be, for example, natural rubber, polybutadiene, styrene-butadiene or poly-chloroprene or an elastomer compound containing one or more of these elastomers.
The filled halobutyl elastomer can be cured to obtain a product, which has improved properties, such as improved abrasion resistance, rolling resistance and traction. Curing can be effected with sulfur. The preferred amount of sulfur is in the range of from 0.3 to 2.0 parts by weight per hundred parts of rubber. An activator, for example zinc oxide, may also be used, in an amount in the range of from 0.5 parts to 2 parts by weight. Other ingredients, for instance stearic acid, antioxidants, or accelerators may also be added to the elastomer prior to curing. Sulphur curing is then effected in any known manner. See, for example, xe2x80x9cRubber Technologyxe2x80x9d, chapter 2, xe2x80x9cThe Compounding and Vulcanization of Rubberxe2x80x9d (3rd ed., Chapman and Hall, 1995).
Other curatives known to cure halobutyl elastomers may also be used. Such known curatives include bis dieneophiles. Suitable bis dieneophiles include m-phenyl-bis-maleinimide and m-phenylene-bis-maleimide (HVA2). Other suitable compounds that are known to cure halobutyl elastomers include phenolic resins, amines, amino acids, peroxides, zinc oxide and the like. Combinations of the aforementioned curatives may also be used.
The mineral filled halobutyl elastomer of the present invention can also be admixed with other elastomers or elastomeric compounds before it is subjected to curing with sulphur. This is discussed further below.